Mice heterozygous for a mutation in the Cbfa1 gene

Mice heterozygous (+/! ) for a mutation in the
Cbfa1 gene on mouse chromosome 17 showlack
of ossification of the skull (2) compared with
normal mice (1). Normal calcified bone is
stained red by alizarin red, here at embryonic
day 17.5, three and a half days before birth. Cartilage
is stained blue by alcian blue. Heterozygous
mice lack a clavicle (4, arrows) in contrast
to normal mice (3).